Drilled and/or slotted is for the most part BS. The only real world advantage MIGHT be slightly reduced unsprung weight. Save your money. The 73 rotor was used on D100 trucks and B100 vans up to whatever year they changed from 5x4.5 to 5x5 bolt pattern. (early 80's) $30-$50 on Rockauto. The slotted ones there are $70 and change.
Pad compound if there are any choices in that application, tire compound and clamping force are your real world variables as far as increased performance over factory specs are concerned. Clamping force with OEM calipers can be tweaked some by playing with master cylinder piston size. The smaller the piston the more pressure you can generate but you also increase pedal travel. Not always a bad thing but needs to be considered with power brakes.
The smallest piston MC come in the 2 bolt style so you would need an adapter to fit your 4 bolt car. IIRC you can get down to a 7/8" piston in a 2 bolt. In a 4 bolt I think 15/16" is available. Cass at Dr. Diff would be the guy to tell you for sure. He may also have caliper bracket kits to fit multi piston calipers like Wilwood or Viper.
I mention tires because they are a critical part of a brake package. If they don't stick, it doesn't matter how big your brakes are.
If you are running power brakes make sure you are using a disc brake specific booster. No ifs ands or buts. For a slab side C-body like yours, 65-68, that means a dual diaphragm booster if it's a column shift car. Floor shifted, the later, larger single diaphragm booster will work but it interferes with the column linkage.
The drum booster doesn't have enough boost to PROPERLY energize OEM Mopar disc brakes. Will it stop with a drum booster? Sure, but it stops now with drum brakes too.
Kevin
